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You Can Surf, but You Can't Hide

MAKING a phone call has always been a game of chance. You never know whether the person you are calling is available. You just punch in the numbers and hope to get lucky.

Imagine being able to learn without dialing a single digit whether another person's phone is in use, or in the case of a cellphone, whether it is even turned on. Now imagine being able to do the same thing with any wired or wireless device of the future -- whether it is in the car, in an airplane or at the gym. Not only could you learn whether a person is available for a chat, but you could also deduce what that person might be doing at that exact moment, all without exchanging a word.

That is the idea behind a programming concept called presence awareness, which is based on the realization that appliances on a network can automatically be detected by other devices.

''The days of phone tag are on the way out,'' said Sonu Aggarwal, chief executive of Cordant, a company in Bellevue, Wash., that develops instant-messaging technology. ''This is a very powerful concept with long-term implications.''

Many software developers predict that presence technology will become almost as ubiquitous as communication devices themselves. In six months, Motorola officials say, the company will roll out a system that will allow a caller to tell whether another person's mobile phone is on and whether it is in use. Nokia and Ericsson, among several other telecommunications companies, are also developing the technology, for use in either land-line or wireless phones.

Presence technology is also being considered for hand-held computers, wireless Web pads, communications systems in cars, and even exercise machines that provide Internet access at the gym. Some systems, the officials say, will go as far as using tracking systems like the Global Positioning System, or G.P.S., to detect the location of a person who is logged in.

The prospect of information that can reveal a person's availability at a given moment, anywhere in the world strikes many people as both creepy and intriguing.

Katelyn Y. A. McKenna, an assistant professor at New York University who conducts research on Internet relationships, has found that people are comforted when they can see the distant movements of people from their inner circles, like family and friends. Devices that use presence technology could provide such reassurance.

''You could see that you could instantaneously reach these people if you need them,'' Dr. McKenna said. ''I know my mother would be extremely reassured if she could see, 'Oh, she's off the plane; her cellphone came on; she's landed.' ''

But along with comfort comes the unnerving feeling of being watched, a lesson that has been experienced by millions of instant messaging users. By keeping track of the activity on their Buddy Lists, people with I.M. can use log-in information to get a sense of their buddies' routines -- when they arrive at work, when they are online at home on a weekend, or in some cases how long they have been away from their computers. Information that was private (or at least not easy to acquire) can become known -- with little effort -- by employers, co-workers, friends, family members and, sometimes, by strangers.

''When you have these technologies you really expose yourself and your day to a lot of people,'' said Bonnie A. Nardi, an anthropologist at Agilent Technologies, a company in Palo Alto, Calif., that makes high-tech monitoring devices.

After spending a few years studying instant messaging, Dr. Nardi said she became aware of the subtle impact of presence technology on people's lives. It is time, she said, to think about ''what we want people to know about what we are doing at a given moment.''

Software programmers and executives have begun talking about how to capitalize on presence technology's potential. For example, at Dynamicsoft, a company in East Hanover, N.J., officials have discussed how presence software, wireless hand-held computers and G.P.S. tracking could alert a person when a friend happened to be a few blocks away. A phone-based system could also automatically plug in teleconference participants the instant everyone in the group was available.

In the future, Mr. Aggarwal of Cordant said, technology might be so integrated that a traveler could wear a wireless badge that interacts with a computer on the back of an airplane seat. When the computer sensed that the traveler was seated, it could automatically redirect messages to the computer's screen or send word to the traveler's contacts that he was on board.

The only widely available version of the technology currently in use is instant messaging. If I.M.'s popularity is any indication, people may be ready to embrace the possibilities of presence detection.

More than 50 million people in the United States use instant-messaging products today, according to industry estimates, and many of those people say that their favorite aspect of the technology is the ability to see whether a buddy is online.

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Still, even some of the technology's adherents acknowledge how strange it is to remotely broadcast their whereabouts. Mr. Aggarwal uses MSN Messenger, which displays a clock icon in the contact list to indicate when a person has not touched the keyboard or mouse for, say, five minutes. As soon as he resumes use of his keyboard or mouse, the clock goes away. Often, he said, he gets a phone calls the minute he hits the keys, and the caller is invariably someone who had been waiting for that icon to disappear.

Hints of a coming struggle between privacy and openness turned up in a recent project at Bell Labs, the research and development arm of Lucent Technologies. In the project, which was called Rear View Mirror, a scientist, Dr. James Herbsleb, and several colleagues studied a group of Lucent employees in American and European offices who used a Bell Labs instant messaging system for more than a year. Privacy issues arose from the start.

He added that they did not like the idea that supervisors could detect -- and therefore monitor -- exactly how long they had been online and how much time they had spent typing on their keyboards.

As a result, Bell Labs researchers altered the software to give users complete control. The program's default options were set to make users appear to be offline. If people wanted co-workers to know they had logged in, they had to turn on the feature that displayed their availability.

That solution did not work very well, Dr. Herbsleb said. The software, which was intended to avoid problems like phone tag, was useless if people had to badger colleagues to announce their availability. Besides, he said, it missed the point of presence technology, which is useful precisely because it senses what is going on without any action by a user.

Ultimately, the researchers and employees compromised. The presence system was automatically turned on for people within small work groups. People outside those groups had to get colleagues' permission to watch their movements. ''Don't allow people to just lurk and spy,'' Dr. Herbsleb said.

But as staying in touch electronically becomes the mark of modern movers and shakers, many people say they will gladly allow their presence to be known in exchange for the convenience of constant contact. ''It's sort of like leaving the front door open, and saying, 'Come on in; don't even knock,' '' said David Wertheimer, who writes a daily Web log called Netwert and is an avid user of instant messaging software.

Software developers say they can design presence awareness systems to accommodate both those who seek privacy and those who want constant contact. Yahoo and Microsoft, for example, include privacy features in their instant messaging products. Users must grant permission before their names can be added to someone's contact list. Instant Messenger, both the stand-alone version and the one embedded in AOL's Internet service, does not allow that level of control. Users have no way of knowing whether someone has added their screen names to a buddy list.

Michele Magazine, a publishing consultant in Manhattan who briefly used the Instant Messenger program from America Online, said she was troubled by the lack of privacy. ''I don't want people to know when I'm at home,'' she said. ''There was no way to hide.''

Whether people will use permission features or other blocking tools is another question. Social pressure can be a powerful disincentive. Some teenagers who use instant messaging programs, for example, said they would not block their peers because they would not want to seem rude.

Consider something like the following alert showing up on your screen: ''Bill wants to put you on his buddy list. Do you accept?'' If Bill is merely a distant acquaintance, and you decline, will it look like a snub? Suppose your girlfriend can tell that you are in your office, using your computer but not your phone. If she decides to call and you don't answer, she may think: ''Why not? Clearly you are available. Are you ignoring me?''

The Internet Engineering Task Force, the group that develops standards for Internet communication, has been thinking about several such implications, according to the engineers involved. One of them is Jonathan Rosenberg, chief scientist for Dynamicsoft and a co-author of the task force's standards for presence and instant messaging technology.

Dr. Rosenberg has come up with an answer for the social dilemma of managing privacy without appearing rude. His idea is appropriately called polite blocking, and it works something like a little white lie. Users could appear to be busy with phone calls when, in fact, they might be blissfully enjoying a few minutes of solitude.

There is another alternative, of course: People could extricate themselves from the technology often enough to keep their contacts guessing. A contact may determine that someone's mobile phone is on -- and it very well may be, but it may also be sitting at home.